The present invention relates generally to a parking brake for use on a self-propelled vehicle. More particularly, the invention relates to a combination automatic parking brake and steering spindle for use in a self-propelled vehicle carrying a elevatable boom or work platform. The present invention utilizes a hollow cylindrical steering spindle as a cylinder for the automatic parking brake.
It is known in the prior art to provide a manually actuated parking brake through a steering yoke or spindle. Those devices are typically used on relatively small hand operated carts and hand operated fork lifts. The parking brake is typically activated by pulling a lever or rotating a threaded rod. Such prior art includes U.S. Pat. No. 2,638,183 which teaches a manual brake extending through a steering yoke and having a "dead man" feature. The user must depress the handle to release the brake and the handle must be kept in its depressed position to operate the dolly. U.S. Pat. No. 3,532,188 also teaches a manually operated brake extending through a steering yoke of a hand operated fork lift. Other similar manually activated brake mechanisms on small carts are shown in U.S. Pat. Nos. 2,775,313, 3,085,285 and U.S. Pat. No. 2,388,692.
The present invention provides an automatic parking brake using as its brake cylinder a tube or cylinder which also serves as a steering spindle for the vehicle. The vehicle is a self-propelled lift carrying an elevatable boom or work platform, typically weighing approximately 3,000 pounds, and capable of carrying up to a 750 pound load. The invention may be readily adapted for use on much heavier vehicles in the range of 12,000 to 15,000 pounds vehicle weight and a working load capacity of 1200 pounds and greater. Additionally, these vehicles are capable of operating on inclines as steep as a 30% incline with its boom or work platform at least partially elevated. These operating conditions and operating vehicle weights and loads require a heavy duty vehicle parking brake.
The parking brake of the present invention is normally engaged by a spring or springs carried in the combination brake cylinder and steering spindle. When the propulsion system for the vehicle is energized, hydraulic pressure enters the brake cylinder and compresses the spring or springs, thereby automatically releasing the parking brake. By utilizing a hollow steering spindle to also form the outer surface of the parking brake cylinder, a reduction in total parts is accomplished. Furthermore, the parking brake is actuated downwardly through the steering spindle and urges the brake pad into contact with the upper surface of a tire. By locating the parking brake cylinder in the steering spindle, minimal hydraulic plumbing is required, since hydraulic plumbing is frequently available at hydraulic motors driving each steerable wheel.
Accordingly, a primary object of the invention is to provide an automatic parking brake for use on a self-propelled vehicle carrying an elevatable boom or work platform, capable of holding relatively heavy self-propelled vehicles on relatively steep inclines.
A further object of the invention is to provide a combination automatic parking brake and steering spindle for use in a self-propelled vehicle wherein the steering spindle also forms the cylinder for the automatic parking brake.
Another object of the invention is to provide an automatic parking brake for a self-propelled vehicle having a relatively simple design with minimum number of components, in part because the parking brake cylinder also acts as a steering spindle.
Yet a further object of the invention is to provide an automatic parking brake for a self-propelled vehicle wherein the cylinder of the parking brake acts as a steering spindle and wherein an enlarged portion of the brake cylinder acts as a thrust bearing to transfer chassis weight of the vehicle to a mounting bracket connected to a steerable wheel.
Another object of the invention is to provide an automatic, heavy duty parking brake for a self-propelled vehicle wherein the brake holding force includes a friction component and a shear component because, when engaged, the brake temporarily deforms a solid rubber tire.
Other objects and advantages will become apparent from the following description and the drawings wherein: